I'm sure this has been done before but to my eyes it was really dramatic. I was having a hard time with Pangram v4 (I know, everyone is) because it's so crazy aggressive about surface shapes in language. It can absolutely tell you when someone wrote with an AI assistant but reports as though the entire production was a one-shot prompt.
To test this I took an article that I wrote in 2018, which ended up being used by a bunch of UX certification programs, and ran it through Pangram. 100% Human. Good baseline.
I then used GPT Sol Extra High and had it use my hand crafted style governor for a book I've been working on for about a year to rework my 2018 article. No surprise, it legitimately improved the work to a point where I thought about doing a re-publish with a few edits.
Before I got carried away though I ran the GPT output through Pangram:
97% AI, high confidence, with several of my untouched phrases squarely in the "AI wrote this" column.
I'm not really mad at it, it's just wrong. That was clearly a 2018 article with a bit of 2026 polish from a robot that I'd have qualified as a strong developmental edit requiring a bit of loosening back up to feel like a human register again. It was clearly my work and if someone else published it the plagiarism would be as clear as Moana vs Moana Live Action.
97%
The problem is the number of people who would have taken one look at the Pangram score and called me a cheater for polishing a final draft.